Deterministic chess program could have done otherwise

A demonstrably deterministic chess program that loses can rightly be said to 'could have castled': it consults a pseudo-random number generator and got a one rather than a zero, so flipping a single bit would have produced the other choice — this is bad luck, not a design flaw, showing that an impeccably designed agent could still have done otherwise half the time or more, with determinism intact.